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Molecular Imaging and Cancer
Cancer causes one in every four deaths in the United
States, second only to heart disease. According to
the American Cancer Society, an estimated 1.6 million new cancer cases were diagnosed and more than
571,950 people died from the disease in 2011.
However, cancer death rates are dropping (by
about one percent annually since 1991), and five-year
survival rates also have increased—to 68 percent, up
from 50 percent in 1975. Both statistics reflect improvements in early detection and treatment.
Molecular imaging has become part of standard
care for many types of cancer. By allowing scientists
and physicians to see what is happening in the body
at a cellular level, molecular imaging provides unique
information to assist in the detection, diagnosis, evaluation, treatment and management of cancer.
What is molecular imaging and how does it
help people with cancer?
Molecular imaging is a type of medical imaging that
provides detailed pictures of what is happening inside
the body at the molecular and cellular level. Where
other diagnostic imaging procedures—such as x-rays,
computed tomography (CT) and ultrasound—predominantly offer anatomical pictures, molecular imaging allows physicians to see how the body is functioning and
to measure its chemical and biological processes.
Molecular imaging offers unique insights into the
human body that enable physicians to personalize patient care. In terms of diagnosis, molecular imaging is
able to:
• provide information that is unattainable with other
imaging technologies or that would require more
invasive procedures such as biopsy or surgery
• identify disease in its earliest stages and determine
the exact location of a tumor, often before symptoms occur or abnormalities can be detected with
other diagnostic tests
As a tool for evaluating and managing the care of
patients, molecular imaging studies help physicians:
• determine the extent or severity of the disease,
including whether it has spread elsewhere in the
body
• select the most effective therapy based on the
unique biologic characteristics of the patient and
the molecular properties of a tumor or other disease
• determine a patient’s response to specific drugs
• accurately assess the effectiveness of a treatment
regimen
• adapt treatment plans quickly in response to changes in cellular activity
• assess disease progression
• identify recurrence of disease and help manage ongoing care
Molecular imaging procedures are noninvasive,
safe and painless.
How does molecular imaging work?
When disease occurs, the biochemical activity of cells
begins to change. For example, cancer cells multiply
at a much faster rate and are more active than normal
cells. Brain cells affected by dementia consume less energy than normal brain cells. Heart cells deprived of
adequate blood flow begin to die.
As disease progresses, this abnormal cellular activity begins to affect body tissue and structures, causing
anatomical changes that may be seen on CT or magnetic resonance (MR) scans. For example, cancer cells
may form a mass or tumor. With the loss of brain cells,
overall brain volume may decrease or affected parts
of the brain may appear different in density than the
normal areas. Similarly, the heart muscle cells that are
affected stop contracting and the overall heart function
deteriorates.
Molecular imaging excels at detecting the cellular
changes that occur early in the course of disease, often
well before structural changes can be seen on CT and
MR images.
Most molecular imaging procedures involve an
imaging device and an imaging agent, or probe. A
variety of imaging agents are used to visualize cellular activity, such as the chemical processes involved in
metabolism, oxygen use or blood flow. In nuclear medicine, which is a branch of molecular imaging, the imaging agent is a radiotracer, a compound that includes
a radioactive atom, or isotope. Other molecular imaging modalities, such as optical imaging and molecular
ultrasound, use a variety of different agents. Magnetic
resonance spectroscopy is able to measure chemical
levels in the body, without the use of an imaging agent.
Once the imaging agent is introduced into the body,
it accumulates in a target organ or attaches to specific
cells. The imaging device detects the imaging agent
and creates pictures that show how it is distributed in
the body. This distribution pattern helps physicians discern how well organs and tissues are functioning.
single set of images. CT imaging uses advanced x-ray
equipment and in some cases a contrast-enhancing material to produce three-dimensional images.
A combined PET-CT study is able to provide detail
on both the anatomy and function of organs and tissues. This is accomplished by superimposing the precise location of abnormal metabolic activity (from PET)
against the detailed anatomic image (from CT).
What molecular imaging technologies are
used for cancer?
How is PET performed?
Positron emission tomography (PET) scans and combination PET and computed tomography (PET/CT) scans
are routinely used to diagnose and treat a variety of
cancers.
What is PET?
PET involves the use of an imaging device (PET scanner) and a radiotracer that is injected into the patient’s
bloodstream. A frequently used PET radiotracer is 18Ffluorodeoxyglucose (FDG), a compound derived from a
simple sugar and a small amount of radioactive fluorine.
Once the FDG radiotracer accumulates in the
body’s tissues and organs, its natural decay includes
emission of tiny particles called positrons that react
with electrons in the body. This reaction, known as annihilation, produces energy in the form of a pair of
photons. The PET scanner, which is able to detect these
photons, creates three-dimensional images that show
how the FDG is distributed in the area of the body being studied.
Areas where a large amount of FDG accumulates,
called “hot spots” because they appear more intense
than surrounding tissue, indicate that a high level of
chemical activity or metabolism is occurring there. Areas of low metabolic activity appear less intense and
are sometimes referred to as “cold spots.” Using these
images and the information they provide, physicians
are able to evaluate how well organs and tissues are
working and to detect abnormalities.
PET-CT is a combination of PET and CT that produces highly detailed views of the body. The combination of two imaging techniques—called co-registration,
fusion imaging or hybrid imaging—allows information
from two different types of scans to be viewed in a
The procedure begins with an intravenous injection of
a radiotracer, such as FDG, which usually takes between 30 and 60 minutes to distribute throughout the
body. The patient is then placed in the PET scanner,
where special detectors are used to create a three-dimensional image of the FDG distribution.
Scans are reviewed and interpreted by a qualified
imaging professional, such as a nuclear medicine physician or radiologist, who shares the results with the
patient’s physician.
How is PET used for cancer?
Physicians use PET and PET-CT studies to:
• diagnose and stage: by determining the exact location of a tumor, the extent or stage of the disease
and whether the cancer has spread in the body
• plan treatment: by selecting the most effective therapy based on the unique molecular properties of
the disease and of the patient’s genetic makeup
• evaluate the effectiveness of treatment: by determining the patient’s response to specific drugs and
ongoing therapy. Based on changes in cellular activity observed on PET-CT images, treatment plans
can be quickly altered
• manage ongoing care: by detecting the recurrence
of cancer
What are the advantages of molecular imaging for cancer patients?
• PET is a powerful tool for diagnosing and determining the stage of many types of cancer, including lung, head and neck, colorectal, esophageal,
lymphoma, melanoma, breast, thyroid, cervical,
pancreatic and brain cancers. The value of PET for
many other cancers is currently being investigated
through the National Oncologic PET Registry.
• By detecting whether lesions are benign or
malignant, PET scans may eliminate the need
for surgical biopsy or identify the optimal biopsy location.
• PET scans help physicians choose the most appropriate treatment plan and assess whether
chemotherapy or other treatments are working
as intended.
• PET scans are currently the most effective
means of detecting a recurrence of cancer.
What are the advantages of molecular
imaging for prostate cancer patients?
When detected early, prostate cancer has more
than a 90 percent cure rate. Because treatment
is highly individualized, molecular imaging technologies are dramatically improving the ways in
which prostate cancer is diagnosed and treated.
With the help of molecular imaging technologies,
physicians are able to select the most effective
therapy, taking into account a tumor’s unique molecular properties. Molecular imaging also allows
physicians to more accurately assess how the disease is progressing.
Scientists also are working on new molecular
imaging techniques that will:
• predict the aggressiveness of a tumor
• predict the outcome of treatment
• detect genetic markers of the disease
• assist physicians in developing even more tailored treatment plans
What are the advantages of molecular
imaging for ovarian cancer patients?
Ovarian cancer is highly curable when treated at
an early stage. However, because there is no effective screening test for the disease, the majority
of women are diagnosed at a late stage when
survival rates are very low. Early detection and
accurate diagnosis are key to increasing ovarian
cancer survival rates.
Researchers believe molecular imaging holds
promise for detecting ovarian cancer before it
spreads into other areas of the body. Studies also
show that hybrid imaging, such as a combined PET-CT scan,
is highly accurate for detecting recurrent ovarian cancer and
for determining the best possible treatment plan.
What are the advantages of molecular imaging for
lung cancer patients?
Molecular imaging is commonly used to improve the diagnosis and treatment of lung cancer. The detailed images provided by PET are able to accurately distinguish between benign
and malignant tumors as small as one centimeter and to differentiate between extensive and limited disease. Information
provided by PET imaging often eliminates the need for exploratory surgery or other invasive medical procedures.
In the future, scientists anticipate that molecular imaging
procedures will be used increasingly to evaluate disease progression, assess treatment strategies and monitor treatment effects.
What are the advantages of molecular imaging for
breast cancer patients?
Physicians are using molecular imaging to determine the aggressiveness of breast disease, to select a course of therapy
and to assess its effectiveness—sometimes after just one cycle
of treatment—and to eliminate unnecessary surgeries after
treatment by distinguishing active tumors from residual masses. Molecular imaging is also used to minimize the removal
of axillary lymph nodes by determining which nodes are most
likely to contain cancer cells. There are many new and emerging molecular imaging technologies that may benefit breast
cancer patients, including:
• combined imaging systems, known as hybrid imaging,
that may improve accuracy and allow physicians to see
how cancer is affecting other systems in the body
• PET imaging biomarkers, such as fluorothymidine (FLT)
to show tumor proliferation and fluoroestrogen (FES) to
detect estrogen receptors
• positron emission mammography (PEM)
• radioimmunotherapy (RIT)
What are the advantages of molecular imaging for
gastrointestinal cancer patients?
For many gastrointestinal cancers, PET-CT is able to identify
where cancer has spread in the body and to assess patient
response to chemotherapy. PET-CT is helpful in nearly all aspects of colorectal cancer diagnosis and treatment, providing
valuable information that directly affects treatment options including: identifying incidental cancers in the colon, staging,
detecting cancer recurrence, distinguishing between cancer
recurrence and post-therapy scarring in the colon, identifying
secondary cancers in the liver or lung, detecting cancer recurrence in patients who have an increased blood protein called
carcinoembryonic antigen Hodgkin’s and non-Hodgkin’s lymphoma and detecting cancer recurrence.
What are the advantages of molecular imaging in
drug development?
In addition to its role in the diagnosis and treatment of cancer,
molecular imaging also serves as a valuable tool in pharmaceutical research and clinical trials.
Molecular imaging is helping scientists gain a better understanding of the basic mechanisms underlying the biology of cancer. Information provided by molecular imaging
technologies has the potential to help the drug development
and approval process become faster, more effective and less
expensive. Researchers are also using molecular imaging
to identify the most promising strategies for developing new
drugs and to design clinical trials to test their effectiveness.
What is the future of molecular imaging and cancer?
Prostate, ovarian and lung cancer are just a few of the many
types of cancer in which molecular imaging can truly change
the direction and outcome of patient care. The ability of molecular imaging to detect abnormalities very early in the progression of disease has the potential to change medicine from
reactive to proactive, detecting and curing disease in its most
treatable phase and saving countless lives.
The material presented in this pamphlet is for informational purposes only and is not intended
as a substitute for discussions between you and your physician. Be sure to consult with your
physician or the nuclear medicine department where the treatment will be performed if you
want more informa­tion about this or other nuclear medicine procedures.
About SNMMI
The Society of Nuclear Medicine and Molecular Imaging (SNMMI) is an international scientific and medical organization dedicated to raising public awareness about nuclear and
molecular imaging and therapy and how they can help provide patients with the best health
care possible. With more than 18,000 members, SNMMI has been a leader in unifying,
advancing and optimizing nuclear medicine and molecular imaging since 1954.
©2012 SNMMI Inc.
Society of Nuclear Medicine and Molecular Imaging
1850 Samuel Morse Drive
Reston, VA 20190
www.snmmi.org
Molecular Imaging and
Cancer